Unit 10- Object Perception

▪ Object agnosia

a failure to recognize objects despite being able to see them

▪ Top-down processing

A process whereby our existing knowledge of objects influences how we perceive them

▪ Bottom-Up Processing

A process whereby physical stimuli influence how we perceive them ▪ What is Recognition?

▪ Perceptual Organization

the process by which multiple objects in the environment are grouped, allowing us to identify multiple objects in complex scenes

o Grouping

the process by which elements in a figure are brought together into a common unit or object

o Segregation

the process of distinguishing two objects as being distinct or discrete

▪ Gestalt Psychology and Perceptual Organization

In terms of vision, Gestalt argues that what we see is greater than its individual parts. That is, the process of perception is designed to see the scene rather than bits of light here and there. Stimuli were sufficiently rich in structure to allow the perceptual system to extract meaning directly from the stimuli rather than building it up from an image of thought. The whole is different from the sum of its parts.

▪ Figure-Ground Organization

the experience viewers have as to which part of an image is in front and which part of an image is in the background of a particular scene

o How Symmetry and convexity affect figure-ground organization. Symmetry

images that are more likely to be seen as a figure and therefore in the foreground, whereas less symmetrical images are more likely to be perceived as background

Convexity

Images with convex borders are more likely to be seen as a figure, whereas those with concave borders are more likely to be seen as the ground. (Stevens and Brookes, 1988)

o Law of good continuation

grouping law stating that edges that are smooth are more likely to be seen as continuous than edges that have abrupt or sharp angles

o Law of proximity

grouping law stating that elements that are close together tend to be perceived as a unified group

o Law of similarity

grouping law stating that elements that are similar to one another tend to be perceived as a unified group

Law of symmetry

grouping law stating that elements that are symmetrical to each other tend to be perceived as a unified group

o Effect of the Common Region and Connectedness

We group objects either because they share a space or are physically linked

▪ Perceptual Interpolation

the process by which the visual system fills in hidden edges and surfaces in order to represent the entirety of a partially visible object

o Edge completion

the perception of a physically absent but inferred edge, allowing us to complete the perception of a partially hidden object ▪ Illusory Contours

▪ How knowledge shapes perception?

Your brain uses past experiences to predict what should be there You’re more likely to see what you expect, even if the visual input is unclear The same image can look different depending on surrounding information Familiar objects are recognized faster and more accurately Mental frameworks (schemas) help you fill in gaps Perception is not just about the eyes—it’s about the brain interpreting information using prior knowledge

▪ Recognition by Components

a theory stating that object recognition occurs by representing each object as a combination of basic units (geons) that make up that object

• we recognize an object by the relation of its geons

o Geons

the basic units of objects, consisting of simple shapes such as cylinders and pyramids o Viewpoint invariance

o Problems with this account

e.g., rectangular prisms

▪ Template theories

theories of pattern recognition which assert that there is a mental representation for each of the patterns to be recognized

o Problems with template theories

Would need a representation of that object from every angle Greater demands on memory Vantage point matters in recognizing

▪ The Neuroanatomy and Physiology of Object Perception

Representation of shapes (and color) in area V4 Object recognition in the inferotemporal (IT) area

o area V4

an area of the brain involved in both color vision and shape perception

o inferotemporal area

the area of the temporal lobe involved in object perception; it receives input from V4 and other areas in the occipital lobe

▪ The Fusiform Face Area and Face Recognition

an area in the inferotemporal area of the temporal lobe that specializes in recognizing familiar faces

• located in the ventral surface of the temporal lobe

o Prosopagnosia

inability to recognize faces but other forms of visual object recognition are relatively intact. For example, a person with prosopagnosia will have difficulty recognizing particular people but will not have difficulty identifying roses or gloves

▪ The Grill-Spector Experiment

examined the role of the FFA in face recognition using functional magnetic resonance imaging (fMRI) technology. participants briefly saw Harrison Ford's face followed by a mask, or a control stimulus followed by a mask (a). In (b), we can see the activity in the FFA when the participant recognized the photo as Harrison Ford and when the participant did not. Note that the highest response in the FFA is for correct recognition.

o Parahippocampal place area (PPA)

an area within the inferotemporal cortex that appears to have the specific function of scene recognition

• tuned for recognition of spatial landscapes, both indoor and outdoor scenes

• screen recognition

▪ Topographic agnosia

a deficit in recognizing spatial landscapes, related to damage to the parahippocampal place area

o Extrastriate body area

an area within the inferotemporal cortex that is activated when its cells view bodies or body parts but not faces

o Grandmother Cells and Specific Coding in the IT Cortex

Theory that there is a particular cell in the ventral processing stream whose job is to fire when you see a particular object or person (such as your grandmother).

▪ The Results of Quiroga et al. (2005)

these data are from single cells within the human temporal cortex. One cell responded to the image of Kobe Bryant but not to the images of other people. Similarly, one cell responded to the image of the Golden Gate Bridge but not to images of other landmarks

▪ The Face Inversion Effect

The inability to detect facial features that are inverted on an inverted face (i.e., the features would be upside down, and very obvious, if the face were turned right-side up), because we are so used to processing faces in the upright orientation.

▪ Capgrass Syndrome

The delusional belief that an acquaintance has been replaced by an identical-looking imposter. It is more commonly seen in schizophrenia, dementia, and brain trauma.

▪ Results of Looser and Wheatley’s (2010) study of animacy

data show participants' perceptions of whether the figures were animate or not (alive or not, realistic or not, have a mind or don't, can feel pain or can't)

• Results showed we have a high criterion for recognizing animacy in a human face.

▪ Accidental Viewpoints

A viewing position that produces some regularity in the visual image that is not present in the world

• Perceptual committees assume viewpoints are not accidental